1. Field of the Invention
This invention relates generally to methods and apparatus for monitoring the presence of a material in a liquid, and more particularly, but not by way of limitation, to methods and apparatus for monitoring the presence in a liquid of a material which is at least partially immiscible in the liquid and which may be induced to form a slick on a surface of the liquid.
2. Description of the Prior Art
Previously issued patents disclose several methods and apparatus for monitoring the presence of a material in a liquid. A patent issued to Gregory et al., U.S. Pat. No. 3,842,270, discloses a method and apparatus for monitoring the presence in an aqueous medium of a material which fluoresces when exposed to ultraviolet light. The apparatus measures the fluorescent radiation caused by directing a beam of ultraviolet light into a falling stream of the aqueous based liquid containing the material to be monitored, and does so by employing visible light detecting means, an amplifier, and a recorder.
Patents to deVial, U.S. Pat. No. 3,965,920, and to Stuart, U.S. Pat. No. 2,263,108, disclose generally similar apparatus. The apparatus in the patent to deVial, as with the device described in the patent to Gregory, et al., employs a chamber having an inlet and an outlet for passing a stream of liquid therethrough, with a beam of ultraviolet light being directed against such a stream and fluorescence detection means for detecting fluorescent radiation produced thereby. Alarm means are also suggested for initiating an alarm when a predetermined level of fluorescent radiation is detected.
The patent to Stuart relates to a method and apparatus for detecting the presence of crude oil in drilling mud being circulated to the top of a well in the course of drilling the well. A beam of ultraviolet light is directed through a transparent window against a surface of the drilling mud returning from the bottom of the well at an angle with respect to the surface. A photosensitive cell is provided for detecting fluorescent emissions from crude oil in the mud.
A patent to Frungel et al., U.S. Pat. No. 3,666,945, discloses another variety of apparatus for monitoring a material in a liquid. In the patent to Frungel et al., a lamp for producing fluorescent radiation from a material and fluorescence detection means for detecting such fluorescent radiation are provided and located in the liquid or medium carrying the material to be monitored.
One problem encountered with devices such as are disclosed in the patents to deVial, Stuart, and Gregory et al. discussed above is the possibility of fouling of the optical equipment in those devices by the liquid or by the material to be monitored. Fouling of the optical equipment can lead to significant distortions in measurements of the material to be monitored, particularly when the material is present only in small concentrations in the liquid and therefore not as easily detected. Moreover, the possibility of fouling is likely increased where the liquid or medium carrying the material to be monitored is of a low viscosity, and therefore likely to be splashed, or where the material to be monitored has a marked affinity for glass or the like, as with oil. Fouling is likely also to be a problem with devices such as that disclosed in the patent to Frungel et al., where the optical equipment is located in the liquid or medium carrying the material to be monitored.
The problem of distorted measurements due to fouling becomes particularly significant when such devices as are discussed above are used to monitor industrial waste water for oleaginous materials and other potential environmental pollutants. It is frequently necessary in the monitoring of such pollutants to be able to monitor the presence of small concentrations of these pollutants, in that such concentrations may be toxic, or may be in excess of federally prescribed effluent guidelines. The fouling of the devices so used could necessitate, under such circumstances, shutting down an otherwise properly operating process until reliable measurements can be obtained to prevent exceeding federal guidelines and to prevent any potential pollution.
In the context of industrial processes involving the repeated or continuous discharge of an effluent stream, it may also be necessary to make a rapid series of tests or measurements to adequately monitor the presence of a pollutant or similar material in the effluent stream. Such might be the case where the flow rate of the effluent stream is high, or where the toxicity of the material is high.
As shown by the above-mentioned disclosures, there is a need for an apparatus and method that permit rapid and repeated monitoring for the presence of a material in a liquid, and that permit accurate monitoring of low concentrations of the material in the liquid.
Accordingly, it is an object of the present invention to provide an apparatus and method fulfilling this need, and which further permit accurate monitoring of low concentrations of the material in the liquid without excessive exposure to fouling.
It is a further object of the present invention to provide an apparatus and method that are easily manufactured, employed, and maintained.
Other objects and advantages will become more fully apparent from a consideration of the following description, the appended claims, and the accompanying drawings.